This invention relates to combustion products detectors of the type having a single ionization chamber with reference and sampling zones therein and a single radioactive source. More particularly, the present invention relates to an electrode assembly for the ionization chamber.
This general type of single-source, single-ionization chamber combustion products detector is disclosed in U.S. Pat. No. 4,044,263, issued on Aug. 23, 1977. That detector includes a conductive housing which forms a first electrode of the system, and a small second electrode disposed within the housing and connected to a radioactive source. A voltage source is applied across these two electrodes, which are connected in series. Interposed between these two electrodes is a third long, thin electrode which is connected to detecting and alarm circuitry, which cooperates with the second electrode to define a reference zone therebetween, and which cooperates with the first electrode to define a sampling or signal zone therebetween.
This arrangement of U.S. Pat. No. 4,044,263 has the disadvantage that the two electrodes disposed within the ionization chamber formed by the conductive housing electrode are of very small area, thereby resulting in reduced sensitivity of the device. Furthermore, the geometry of these electrodes is such that there is negligible isolation of the reference zone from the sampling zone of the ionization chamber. Thereby further limiting the sensitivity and precision of the instrument. It is known to use instead of these two inner electrodes of U.S. Pat. No. 4,044,263, two small conductive rings separated by an insulator. But such rings also have a very small conductive area and remain relatively ineffective in providing isolation of the reference zone of the ionization chamber.
Furthermore, the prior art systems of the type disclosed in U.S. Pat. No. 4,044,263 have a relatively bulky ionization chamber which may be several inches in depth and in excess of six inches in width, and the other electronic circuit components are typically mounted outside the ionization chamber. When the other bulky components of the system such as audio signal generator, batteries and the like are added, there results a relatively large overall package.
A further disadvantage of these prior art systems is that assembly of the ionization chamber and the electrodes therein requires the use of a number of fasteners and associated tools, thereby adding to the overall cost of manufacturing the unit.
The aforementioned prior art is the most pertinent prior art known to the applicant, and U.S. Pat. No. 4,044,263, copy of which is filed herewith, is the most pertinent printed publication known to applicant which discloses such prior art.